Dairy farmers were soon being paid less than it cost to produce the milk. Moreover, farmers were told prices were backdated and they would need to pay back the difference -- about $200 million between 2,500 farmers -- according to the ABC.

New Zealand dairy company Fonterra soon slashed its prices as well.

Dairy farmer Kathleen Johnston is selling her New South Wales farm after her family worked out they would be losing $70,000 a year under the new prices.

"The very minute that we got the letter that said that's what the price is going to be, we decided, 'no, we can't keep going like this', that we would finish up," Ms Johnston told Four Corners.

Lawyer David Burstyner is in discussions to launch a class action on behalf of dairy farmers.

"I ask myself the question: why does a processor think it can get away with retrospectively changing the price, with clawing back money already paid for a product?" Burstyner told the ABC.

"I've looked at the contracts. I see no clear right to it. I've listened to the statements that have been said for ten months as to the price that will be paid, and the only answer I can come up with as to why the company does it is that they don't ask themselves, 'Is it legal?' They ask themselves, 'Can I get away with it?'"

Prime Minister Malcolm Turnbull and Deputy Prime Minister Barnaby Joyce will be meeting with Murray Goulburn management in Canberra on Tuesday, and Fonterra next week.